1. Field of the invention
The present invention concerns a method and device for detecting the speed of transmission and checking the template of digital messages transmitted to a receiver device over a transmission line.
It applies more particularly to receiving asynchronous digital transmissions when it is necessary to verify the information received conforms to one predefined modulation templates each specifying constraints to be applied to a number of transmission parameters, such as:
the duration of transmission of one information bit PA1 the duty factor of the modulation signal; PA1 the time interval or "Gap" between two words; PA1 the number of bits per word; and PA1 the parity of the word. PA1 a first step of coding beforehand a particular number of possible templates definable by a limited number of parameters; PA1 a second step of detecting said parameters in the information being received and determining which of the memorized templates matches the detected parameters; PA1 a third step of checking that the information received conforms to the detected template; PA1 returning to the second step if said checking indicates that the information being received does not conform to the detected template. PA1 Of course, a method in accordance with the invention could further provide for the rejection of unreliable information, that is say information which during its transmission did not meet all of the constraints of a single template from all possible templates. PA1 cyclical scanning at a fixed frequency of a programmed list of conditions stored in memory; PA1 acquisition of information transmitted on the line PA1 activation of a selection process each time that the information selection criterion has been acquired, the selection process including a synchronization stage which waits for the scanning process to cross the start of said list of conditions, a comparison (pattern matching) sequence on the selection contained in the information being received and the production of a selection variable which indicates the message being received is of interest to the receiver or not, the selection process ending either when all the conditions from said list have been exhausted and on returning to the start of list condition or upon reading a special end of list code; PA1 memorization of the information selected in a buffer accessible to said local unit. PA1 a first step of coding beforehand a particular number of possible templates definable by a limited number of parameters; PA1 a second step of detecting said parameters in the information being received and determining which of the memorized templates matches the detected parameters; PA1 a third step of checking that the information received conforms to the detected template; PA1 returning to the second step if said checking indicates that the information being received does not conform To the detected template. PA1 a first number on eight bits (bits 0 through 7) defining a label; PA1 a second number (SDI) on two bits (bits 8 and 9) identifying the source or the destination of the word; PA1 a third number on 21 bits (bits 10 through 30) containing the transmitted data; and PA1 a parity bit (bit 31).